In __canonicalize_path() we only call stat() to know if the path
is a link or not. When the filesystem doesn't support links we
already know that it's not a link, so we do not need to call stat().
This helps the tftp filesystem since the parent directories of
a file to be opened won't be stat()ed anymore, something tftp
does not support.

Fixes: a602bebc fs: Implement links to directories

Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>